1. Field of the Invention
This invention relates generally to disposable filters for fluid streams, and more particularly to extended surface area filters or pocket filters. The invention further relates to a pocket filter having a reusable frame and replaceable filtration media. The invention additionally relates to a pocket filter that is easily constructed from a single piece of filtration media. Moreover, this invention relates to a method of using the pocket filters of this invention in combination with planar filters to: (a) control the air flow or holding capacity over the fluid flow area of the fluid handling device; and (b) adjust the type and variety of filters which extend across the fluid flow area to control the change-out schedule of the individual filters. The filters of this invention and the described method of use may be used in association with a spray paint booth, a heating system, a ventilating system, an air handling system, an air conditioning system, or any other area which needs filtration.
2. Description of the Related Art
Many materials and combinations of materials have been used as filtration media to remove solid or liquid particulate from fluid (i.e. liquid or gaseous) streams. The capabilities of such filter media are judged according to three main criteria: (1) the particulate removal efficiency (i.e. the ability of the filter media to capture and retain particulate); (2) the pressure drop for a given flow rate of fluid through the media (which is utilized as a measure of the power required to move the fluid stream through the media); and (3) the holding capacity or the total amount of particulate which can be retained by the media before the pressure drop becomes so great that the media must be cleaned or replaced.
One solution to improving the performance of a filter system known commonly in the prior art is to arrange filter media into extended surface area configurations commonly known as pocket filters. By increasing the amount of filter media presented to a given fluid stream, the fluid flow through a unit area of the media is reduced, consequently lowering the total pressure drop through the filter arrangement (i.e., lowering the power required to move the fluid stream). Furthermore, by using an extended surface area configuration to increase the area of filter media present to a given flow area, greater amounts of particulate can be accumulated before the resultant pressure drop increase requires the filter media to be cleaned or replaced. Moreover, it is known in the prior art that the greater the number of pockets in a pocket filter, the greater the effect because more filter media is possible with more pockets. These capability improvements are achieved for any given filter media and as such the particulate removal efficiency remains relatively unchanged in a pocket filter as compared to the same filter media used in a flat or planar filter. Consequently, for a given filter media, the use of a pocket filter can create a filter system with nearly the same efficiency as a planar filter yet, as a system, requires less power for the movement of the fluid stream, and has a longer life.
It is also known in the prior art that, generally speaking, more efficient filter medias have higher per unit pressure drops. Therefore, by arranging more efficient filter medias in extended surface area configurations yields filters having increased efficiencies with no more pressure drop than their lesser efficiency planar filter counterparts.
In order to achieve the advantages of a pocket filter, filter media must be arranged, supported, retained and sealed in place by frames and/or other structural systems. In the prior art, such structural systems include: (1) wire frames around which the edges of the pocket filter media are wrapped and then sewn, glued, heat sealed, stapled or otherwise permanently attached to the frame; and (2) metal or plastic channel-type frames that clamp or otherwise mechanically attach around the edges of the media pockets to form a pocket filter assembly. In the prior art, much effort has been put to improving the structural systems for extended surface area filters. One such improvement is shown in U.S. Pat. No. 4,300,927 which describes a frame for a pocket filter. Another such improvement in pocket filter frames is shown in U.S. Pat. No. 4,325,718. Yet another improvement for pocket filter frames is disclosed in U.S. Pat. No. 5,298,044.
Further, prior art pocket filters have been constructed with a single V-shaped pocket, multiple V-shaped pockets, or cube shaped pockets. In those cases, the filter media is permanently attached to the frame around the perimeter of the filter entrance plane with the pocket or pockets hanging from the frame on the downstream side of the frame. In the case of multiple V-shaped pocket filters, the filter media pockets are also supported in the filter entrance plane by an interior portion of the frame located at the peaks between adjacent pockets. In all prior art pocket filters known to the inventor, the filter media tapers away from the frame components such that all parts of the media are directly exposed to the straight-line fluid flow.
The prior art described above demonstrates the current state of the art of extended surface area pocket filters and the complexity and cost associated with the products. The cost of these items is of particular interest when the prior art pocket filters are designed to be disposable (i.e., non-cleanable) because the frame is an integral part of the filter assembly and must be disposed of with, and when, the dirty media is disposed, thereby increasing the cost of each replacement filter unit. Disposal is further complicated and costly in that the frames are generally of a different material than the filter media (e.g., metal frames vs. fibrous medias). Solid waste disposal (verses incineration for example) is generally the only option available when multiple materials are present.
Another problem with the prior art filters is that the frame is permanently attached to the filter media at the factory meaning that the frame dictates shipping size and shipping cost. Larger filter units become cost prohibitive in shipping size due to the large frame size. Frame dimensions are generally limited to smaller parcel package sizes. Typically these frame dimensions are found to be 20″×20″, 24″×24″ and occasionally, 24″×48″. As can be appreciated, the complexity and cost to manufacture many smaller pocket filters is greater than the cost to manufacture fewer larger pocket filters. A further consequence of the smaller filter unit sizes is the greater time and therefore the greater cost associated with the change-out of many smaller pocket filters (as required by the increased pressure drop resulting from the accumulation of captured particulate) in a large filter bank as compared to fewer larger pocket filters. As an example, the filter bank in a typical spray booth measuring ten feet high by twenty feet wide would require fifty 24″×24″ pocket filter units to be changed. Furthermore, by comparison, the same ten foot high by twenty foot wide spray booth would easily require ten or less pocket filters of the current invention. It must also be understood that for the pocket filters to perform the required function of filtering particulate from the fluid stream the pocket filters must be properly installed in the filter bank. It is certainly easier and therefore more dependable to install fewer larger pocket filters than it is to install a greater number of smaller pocket filters.
It is a further problem with prior art disposable pocket filters that in order to keep costs down, the strength and durability of the frame must be minimized. It is very common in the prior art that, unless carefully handled, the frames within a disposable pocket filter will be damaged or deformed during shipping and installation. If such damage occurs, the functionality and the dependability of the pocket filter are compromised.